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Maxim > Design Support > Technical Documents > Application Notes > High-Speed Interconnect > APP 4211
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Keywords: EMI, EMC, SerDes, serializer, deserializer, automotive, pixel, bulk current injection, BCI, RKE,
remote keyless entry, grounding, bypassing, PLL, LVDS, matched impedance, DC-balanced, common-
mode choke, ferrite bead, differential pair, CAT5
APPLICATION NOTE 4211
EMI-/EMC-Ready SerDes—Basic Test Strategies
and Guidelines
Dec 15, 2010
Abstract: Electromagnetic interference (EMI) and electromagnetic compatibility (EMC) testing is an
important part of design verification for serializer/deserializer (SerDes) devices in automotive
applications. EMI and EMC must be considered early in the design cycle to prevent needless design
revisions. The following application note details helpful, basic concepts and guidelines on how to prepare
your SerDes system for EMI/EMC testing.
A similar version of this article was published August 3, 2009 on AutoElectronics-online by Electronic
Design.
Introduction
LCD video displays are becoming increasingly more common in automotive applications. Rugged design,
small size, and low cost make them ideal for safety, navigation, and infotainment systems. LCD displays
are digital and operate with discrete digital values for each pixel. Because the media/graphic sources that
drive these displays are also usually digital, a digital link is the simplest and highest performance method
to interface a video source with the display. The digital channel for this video link must provide a high
bandwidth. For example, a 640 x 480-pixel color display operates at 30fps (frames per second). With
only 6-bit resolution for each red, green, and blue pixel, the corresponding data rate is 640 x 480 x 30 x
18 = 166Mbps. The actual transmit speed must be one bit faster, as blanking times are required for
proper operation. Many displays have many more pixels and/or a larger number of pixels per bit, quickly
escalating this bit rate. Serializer/deserializer (SerDes) chipsets then take the parallel digital data and
serialize it for transmission. Some devices, such as the MAX9209 serializer, keep the red, green, and
blue data separate, resulting in one serial channel for each of the three primary colors, plus a fourth
channel for the clock. Other devices, such as the MAX9247 serializer, combine this data into a single
serial channel with an embedded clock signal. Both of these approaches increase the fundamental
frequency of the transmission significantly. Although the increase in frequency can cause problems, it is
easy to provide a properly shielded and impedance-matched transmission medium for the serialized
signal.
EMI Testing
EMI testing is necessary in automotive applications to ensure that select systems do not corrupt the
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